Encapsulated transformer



Jan. 26, 1965 w. J. NOVAK ENCAPSULATED TRANSFORMER 5 Sheets-Sheet 1 Original Filed Oct. 15, 1959 INVENTOR. W/ll/AM NOV/1K BY X7 2 2 Jan. 26, 1965 w. J. NOVAK ENCAPSULATED TRANSFORMER Original Filed Oct. 15, 1959 3 Sheets-Sheet 2 INVENTOR.

W/lZ/AM NOVA/f BY W Jan. 26, 1965 W. J, NOVAK ENCAPSULATED TRANSFORMER Original Filed Oct. 15, 1959 3 Sheets-Sheet 3 INVENTOR. W/Ll/AM J. NOV/1A f zwm/ United States Patent This invention relates to power distribution transformers, and more particularly relates to transformers wherein the usual construction including a steel tank filled with insulating oil has been dispensed with in favor of a completely encapsulated transformer in which the insulation function is provided by materials which in their final state are solid rather than liquid, this application being a division of application Serial No. 846,678, filed October 15, 1959, now United States Patent 2,975,385.

The advantages of a dry type of transformer construction are quite numerous and significant insofar as the user is concerned, and such dry type transformers can be manufactured at a cost which is substantially the same as that of an oil filled type. In general, the advantages which may be realized from a dry type of transformer construction are, firstly, that such a transformer can be made to be substantially lighter in weight and smaller in size than an equivalent capacity oil filled type so that installation of the transformer on a mounting pole may be much more easily effected. For example, whereas oil filled transformers of a particular kva. rating may weight about 450 pounds, the equivalently rated dry type of transformer according to my invention may weigh about 300 pounds and occupy only about25% of the volume of the-oil filled type.

Secondly, the noise level can be made very low because the encapsulation of the transformer, subsequently to be described, almost completely eliminates vibration of the steel corelaminations. Additionally, the absence of the insulating oil permits the transformer to be made in a much smaller physical size, and, of course, there is no insulating oil which may deteriorate because of contamination. Maintenance problems are, of course, reduced because there are no exposed metal parts requiring painting, and the encapsulation process prevents transformer outages caused by short circuits between the live terminals and the casework through the bodies of birds and small animals. Finally, when the encapsulation process is carried out by employing a non-hygroscopic outer plastic coating, the entire transformer is rendered much less susceptible to breakdown in wet or damp environments by preventing moisture from penetrating into the coil structures. Accordingly, it is a primary object of my inven tion to provide a power distribution transformer which does not rely upon an oil tank in which transformers of this type are usually housed, but is instead a dry type of transformer.

It is another object of my invention to provide a novel power distribution transformer which is relatively light in weight and small in size by comparison with an equivalent capacity oil immersed transformer.

Still a further object of my invention is to provide a novel power distribution transformer which is characterized by a relatively low noise level due to the fact that the transformer core laminations are restrained'from vibration by an encapsulating plastic composition.

Yet another object of myinvention is to provide a novel power distribution transformer which is less subject to electrical breakdown than a comparable capacity transformer of conventional design by employing a dielectric insulating material not subject to contamination in use. The foregoing and other objects of my invention will 3,lti?,732

all

become apparent from a careful reading of the following specification taken in conjunction with an examination of the appended drawings, wherein:

FIGURE 1 is a front perspective view of a typical transformer according to the invention fragmented to enlarge the scale and having some portions of the exterior broken away to reveal certain constructional details;

FIGURE 2 is a fragmented cross-sectional view through the bottom of the transformer of FIGURE 1 as viewed along the lines 2-2 of that figure;

FIGURE 3 is a fragmented cross-sectional view taken through the transformer of FIGURE 1 along the lines 33 of that figure; of that figure;

FIGURE 4 is a fragmentary perspective view of the upper part of the transformer of FIGURE 1, with a portion thereof sectioned away to reveal certain of the constructional details thereof;

FIGURE 5 is a partial perspective view of the core and coil assembly of the transformer of FIGURE 1;

FIGURE 6 is an enlarged detail of the area within the phantom lines of FIGURE 5 and illustrates the construction of each of the transformer coils;

FIGURE 7 is a perspective view in section through the ransformer core and coil assembly and is taken through such assembly along the lines 7-7 as indicated in FIG- URE 5;

FIGURE 8 is a sectional view taken through the transformer core and coil assembly as would be seen when viewed along lines 8-45 of FIGURE 7.

In the several figures like elements are denoted by like reference characters.

A gross understanding of the transformer structure will best be had by referring first to FIGURE 1. As best seen in the showing of FIGURE 1, the basic transformer includes upper and lower core housings 38 and 34, the coil pressure pads 33 seated upon the flanges of the lower core housing 34 and upon which in turn rest a pair of side by side composite coil structures generally indicated as at ZG-Zt) disposed about parallel legs of a laminated core structure 30, high voltage and low voltage bushing assemblies including the inverted L-shaped brackets 36 and 37, and the bushings 43 and 44, clamping stud assembly 4:), lifting lugs 48, and support lugs 49. The coil assemblies 2t}20 illustrated in FIGURE 1 are identical to one another and the make-up thereof will be described subsequently in connection with the showing of FIGURE 6. However, before proceeding to a detailed description of the coil structures -40, it will be more conducive to a complete understanding of the invention to first consider the method of assembling the entire transformer by assuming that the coil structures 2il-20 have already been pro-formed and are ready for assembly with the other transformer components.

As best seen from the showings of FIGURES l and 2, the lower core housing 34 is U-shaped in cross section having a bottom wall 50 and a pair of vertically extending front and rearwalls 5'1 and 52 respectively. Turned outwardly from the front and rear walls 51 and 52 are a pair of flanges 53 to provide a base upon which are seated the front and rear coil pressure pads 33. It should be observed that the spacing between the front and rear walls 51 and 52 of the lower core housing 34 is just sufficient to accommodate the depth of the laminated core 3%), the core being seated upon the bottom wall 52 of the lower core housing 34. As best seen in the showings of FIGURES 1 and 3, the front and rear walls 51 and 52 of the lower core housing 34 are of generally trapezoidal shape having the smaller trapezoidal base merging with the bottom'wall 59 and the longer trapezoi dal base being the one from which the pressure pads supporting flanges 53 are turned out. Welded or otherwise the preformed coils 2li20, the banding straps 31 and.

the banding seals 32. The composite core and coil structure is assembled in the manner which will be most readily understood by referring firstly to FIGURE 7 and then to FIGURE 1. Referring first to FIGURE 7, it is observed that the core is composed of an upper G-shaped section 65 and a lower C-shape'd section 61. The coil assemblies ZtL-Ztl may be first slipped downwardly over the upwardly extending legs of the core lower section 65., and the core upper section 60 may then be placed in the position illustrated by projecting the downwardly extending legs thereof into the central openings of the preformed coil structures to form a complete core having each of its side legs disposed within a coil. As best seen in FY- URE l, the banding straps 31 are then placed around the two core sections vand tightly secured by means of the banding seals 32. The composite core randflcoil structure so formed is now placed within the lower core housing 34- by seating the bottom of the core lower section 61 between the front and rear walls 51 and 52 of the 7 lower core housing 34, with the coil structures 2.20 seated upon the coil pressure pads 313.

Cf course, the composite core and coil assembly could have been formed in other ways, as for example by winding a continuous strip core through the central window openings of the coil structures so that the resultant core would not be characterized by having an upper section 6i and a lower section 61.

With the composite core and coil structures seated with in the lower core housing 34, the high voltage bushing assemblies including the bracket 36 and bushings 43, and the low voltage bushing assemblies including the bracket 37 and bushings 44 are placed in position as illustrated in FIGURE 1, the high voltage and low voltage leads and 39 respectively extending from the coils are connected to the bushings, and the upper core housing 38 is placed in position.

to thereby securely clamp the entire assembly together.

blies. Welded or otherwise secured to the ends of the upper core housing 33 are a pair of angle brackets much the same as the angle brackets 54 associated with the lower core'housing. Theangle brackets 56 restrainf ingly engage an upwardly projecting shoulder 57 formed on the high voltage bushing element 36 to prevent the 1 element 36 from-tending to slip sideways out from under thevertical compressional clamping provided by the angle b'rackets 56. Similarly, a pair of projections 58 formed onthe'lowvoltage bushing assembly element 37 extend upwardly through complementally formed apertures in the front flange of the upper core housing 38.

Welded onto the front and rear faces of the upper core housing 38 are a plurality of lifting'lugs 48 which are utilizedduring transformer installation to elevate the trans- Also I the support lugs 49 which are employed to firmly secure the transformer in its installed position. The entire transformer assembly of FIGURE 1, secured together in the manner described, is then placed in a potting tank and completely encapsulated by a suitable plastic composition excepting for the lifting lugs 43, the support lugs 49 and the terminals of the high and low' voltage bushings 43 and 4 5. The encapsulation of the transformer causes the plastic potting composition to penetrate into all of the openings of the assembly, as for example into the upper and lower core housings 38 and 34, between the coil assemblies 2t -2ti and the core 34 resulting in a finished transformer.

FIGURE 4 illustrates a fragmentary sectional perspectivc view of the encapsulated transformer showing various parts described in connection with the showing of FIG- URE l and their relative locations within the encapsulating plastic coating The illustration of FIGURE 5 shows the two pre-formed coil assemblies on the core, and the detailed construction of an individual coil assembly 26 will now be described in connection with theshowing of FIGURE 6 to which reference should be had.

The pre-formed coil structure of FIGURE 6 is builtup by first placing the high voltage winding 22 about the coil form 21 and then varnish dipping the high voltage windingZZ on its coil form 21 toprovide the enclosing coating 23. Next, the low voltage coil form 24 is wrapped about the varnish dipped high voltage winding unit and the low voltage winding 25 is built-up. This entire build is now potted within the enclosing plastic coating 26.

Thus, as seen in FIGURE 8, the varnish coating 23 appears as two radially separate layers, the first varnish layer lying immediately radially inward of the coil'form 21 while the second varnish layer lies immediately radially outward of the high voltage winding 22. The plastic coating 26 appears in a similar manner, an inner layer ,lying immediately radially inward of the first varnish layer while the outer layer lies immediately radially outwardof thelowvoltage winding 25. The insulating layer 2? is wrapped about the built coil'structure which may then be asembled to the core in the manner already described. The final plastic coat 28 is that which results from the encapsulation of the entire transformer as also previously described. The coil form and insulating layers 21, 24- and 27 may typicallyrbe one-eighth inch thick silicone rubber made by the Dow Corning Company and identified as Silastic RTV, polyester glass laminate made by the Glastic Corporation and built-up to a thickness of one-eighth of an inch, or any other suitable material. The coil windings 22 and 25 may be made of copper or aluminum magnet wire or foil insulated with a class B' or higher rated insulation. Thevarnish dip layer 23 could suitably be a ten mil maximum thickness layer of Westinghouse B- varnish. The plastic potting layers 26 and 28 .are' preferably formed from a weather resistent insulating material of class B rating or higher, as for example the epoxy resin identified as Epon manufactuned by the Shell Oil Company. The foregoing materials are, of course, listed merely by way of illustration, and other suitable materials may be just as readily employed depending upon personal preference or particular application.

The major transformer mechanical components illustrated in FIGURE 1, such as'theupper and lower core housings 33 and 34, the angle members 55 and 56, clamping stud assembly 49, and lifting and supporting lugs 43 g and 49 will generally be made of steel, whereas the high and low voltage bushing assembly elements with the exception of the terminals will generally be formed of porcelain, and the coil pressure pads 33 will be formed of a class B insulating material such 'as a polyester fiber glass. p T

apparent that variations andmodiiications' will naturally occur from time to time to those persons normally skilled in the art without departing from the essential spirit or scope of my invention, and accordingly, it is desired to claim the same broadly as well as specifically as indicated by the appended claims.

What is claimed as new and useful is:

1. In an electrical power distribution transformer, a preformed coil structure disposed about one leg of the transformer core and including both high voltage and low voltage windings comprising, a high voltage winding wound upon a first electrical insulator coil form, said high voltage winding and first coil form having a varnish coating thereon to form a sealed unit, a second electrical insulator coil form wrapped closely about said sealed unit and a low voltage winding wound thereupon, said low voltage winding and second coil form and sealed unit being bonded together with a hardsetting weather-resistant plastic composition to form a completely encapsulated pro-formed coil structure.

2. A pie-formed coil structure for an electrical power distribution transformer, said coil structure being of generally square cross-sectional shape and having a substantialiy square core receiving window centrally located therein, said coil structure comprising concentric radially disposed adjacent layers, the innermost and outermost layers being part of an outer encapsulating shell made of a weather-resistant plastic insulation material, the layers extending radially outward between the innermost and outermost layers being in order, a first varnish layer, a first coil form barrier layer of electrical insulating material, a first electrically conductive winding, a second varnish layer, a second barrier layer of electrical insulating material, and a second electrically conductive winding, said first and second varnish layers being part of an inner shell which encapsulates said first barrier layer and first electrically conductive winding.

3. The pro-formed coil structure according to claim 2 wherein said first winding has a greater number of turns than said second winding.

4. An electrical power distribution transformer including a core having a pair of parallel extending legs, a pair of identical pro-formed coil structures each of which is disposed about a different one of said pair or" parallel core legs, each rare-formed coil structure comprising a high voltage winding wound upon a first electrical insulator coil form, said high voltage winding and first coil form having a varnish coating t ereon to form a seaied unit, a second ciectrrcal insulator coil-form wrapped closely about said sealed unit and a low voitagc winding wound thereupon, said low voltage winding and second coil form and sealed unit being bonded togetherd by a hardsetting plastic encapsulating composition to complete the said pro-formed coil structure, each of said pre-forrned coil structures being further enclosed by a barrier layer of el ctrical insulating material, and the core and enciosed pro-formed coil structures being bonded together and encapsulated by a hardsetting weather-resistant plastic composition which fills all void spaces in the com posite core and coil structure.

References Cited by the Examiner UNITED STf TIES P TENTS 430,972 4/89 Thomson 336-212 1,303,511 5/19 Shackelton 336-205 2,479,400 8/49 Pecaroni et ai 336205 X 2,925,570 2/60 Strock 33696 2,948,930 8/60 Herbst 336-96 X 2,978,659 4/61 VVahlgren 336-96 3,(,=t;7,125 10/61 Furbee 36-96 X 3,643,994 7/62 Anderson 33696 X LARAMIE E. ASKIN, Primary Examiner. ORIS L. RADER, E. JAMES SAX, JOHN F. BURNS,

Examiners. 

1. IN AN ELECTRICAL POWER DISTRIBUTION TRANSFORMER, A PRE-FORMED COIL STRUCTURE DISPOSED ABOUT ONE LEG OF THE TRANSFORMER CORE AND INCLUDING BOTH HIGH VOLTAGE AND LOW VOLTAGE WINDINGS COMPRISING, A HIGH VOLTAGE WINDING WOUND UPON A FIRST ELECTRICAL INSULATOR COIL FORM, SAID HIGH VOLTAGE WINDING AND FIRST COIL FORM HAVING A VARNISH COATING THEREON TO FORM A SEALED UNIT, A SECOND ELECTRICAL INSULATOR COIL FORM WRAPPED CLOSELY ABOUT SAID SEALED UNIT AND A LOW VOLTAGE WINDING WOUND THEREUPON, SAID LOW VOLTAGE WINDING AND SECOND COIL FORM AND SEALED UNIT BEING BONDED TOGETHER WITH A HARDSETTING WEATHER-RESISTANT PLASTIC COMPOSITION TO FORM A COMPLETELY ENCAPSULATED PRE-FORMED COIL STRUCTURE. 